The present invention relates to an electromagnetic injector or internal combustion engine fuel injection systems.
Injectors of the aforementioned type normally comprise a body with a nozzle which, for injecting fuel, is opened by a control valve which connects the control chamber of the nozzle to a drain conduit. The nozzle is normally closed by a plunger and the fuel pressure inside the control chamber, and is opened by the control valve reducing the pressure inside the chamber and raising the plunger.
The control valve on known injectors normally comprises a ball cooperating with a conical seat in a hole connecting the control chamber to the drain conduit. Control valves of the aforementioned type present numerous drawbacks. Firstly, contact between he ball and the conical seat occurs entirely about a circumference, so that, to ensure sealing between the two, both the ball and seat must be machined to a high degree of precision, which obviously increases the cost of the injector. Secondly, due to the severe pressure involved, such a connection is invariably subject to a certain amount of leakage on account of the shallow contact surface between the ball and the conical surface.
Finally, due to wear, the ball tends to rut the conical surface, forming an impression or recess, which results in a variation of the surface of the ball exposed to the fuel pressure and, consequently, in the thrust of the ball in the direction of the return spring, thus impairing operation of the injector.